When is a lead-acid dead!

In an email it was asked:

"You may be able to solve a problem that has bugged me, and the charity where I work as a volunteer, for ages. The charity loans electric scooters and powerchairs to disabled people to use in the local shopping areas of our home town. Many of our users have their own machines and frequently tell me that they have had to buy new batteries (2 x 12 Volt 38 - 44 Ah gel batteries at around £150.00 and above the pair) because following a service 'it was found that the batteries were duff'

"I have not needed to check our fleet of 24 electrical powered machines since I let it be known to the previous firm that did the servicing of the machines (needed for insurance purposes) that I had marked all the batteries with a UV pen, and told the new firm the same! Funny innit!

"Can you outline a test that I can carry out on these types of batteries to prove or disprove whether they are actually duff or not, even if it entails purchasing test equipment other than my digital multimeter?"

What was not clear was whether it was during a service it was stated the batteries were duff (much like a motor-mac telling you the engine needs an overhaul - even though it doesn't - when you've simply asked for the oil to be changed), or if it is after a service there is suddenly a battery problem. But, whether it was a case of the guy simply trying to get more money from battery sales, or nicking the batteries for other uses (replacing the good ones with duff ones), taking the elderly for a ride is despicable!

When it comes to batteries there is no simple test one can do with a multimeter. There are a number of aspects to batteries and battery life, and a multimeter could lead you up the garden path and then slam the door in your face. When thinking gel batteries, think standard lead-acid car battery. It's the same technology, just a different version of acid.

Such scooters will demand two things, high current spurts (while maintaining the voltage) to move the scooter, and then a reasonable capacity to keep doing this a few times a day at least. Such scooters usually have some form of a meter on the handlebars, so a multimeter is merely emulating this (albeit a little more accurately) and therefore pretty useless.

The best item for testing a battery is likely to be available at your local motor spares place. As the amp-hours matches a motorcar battery pretty closely, it will work a treat. The whole idea will be it will test the capacity and current delivery capability of the battery, and give you a rough indication of its condition.

Alongside is a picture of one (although more sophisticated are on the market) that shows the voltage of the battery before and after load is put on it. Any motor-spares place should be able to offer you a range of such testers. These have even been seen advertised in 'household item' catalogues that come out every so often.

A relatively simple test follows, although not in itself complete it does indicate if further testing is required.

There are two aspects to such battery systems, the first is the batteries, the second is the charging system. Without a decent charge, the battery could appear to be duff!

At the end of a full night's charge, using an accurate digital multimeter (ok, so it's not all useless), check the voltage on each battery is not beyond 14.0V while the charger is still plugged in. If above this then it can be almost guaranteed the batteries are being over-charged and their life shortened (the acid 'dries out').

The difference in the voltage of each battery should not be more than 0.25V between them. If more, this indicates a difference in the health of the batteries. It would not be considered a waste of time consulting the battery manufacturer for their charging specs, which varies by altitude and temperature.

Unplug the charger and allow the battery to stand unused for a half hour. The battery voltage should not fall below 13.2V. Then place a load on the battery (using the tester) for about 30 seconds and if the voltage starts to drop away then the plates cannot deliver the current.

A simpler test could be to use the scooter itself as the load if one can accept the disadvantage of the scooter moving. If the handlebar meter dips badly as the scooter pulls away, then this is indicative of the battery starting to give up the ghost. This shows it is no longer capable of supplying the current required. Even though the actual electrolyte may have all the capacity (the stated 38..44Ah) the plates in the battery are starting to deplete - although do pay attention to probable dirty contacts that can show similar symptoms.

If the current can be delivered, leave the battery for a day with no use and the voltage should not drop more than 0.25V. If it does then the acid is starting to break down and become conductive thus self-discharging the battery.

If proved the batteries are ok, now comes a trick. It was devised after having been at the centre of similar disputes where it was found that similar maintenance free batteries were suddenly failing at radio installations.

It was asked that the date simply be written on the battery, but that a secret letter also be stamped on. The date looks ominous so it was copied, however, most ignored the stamp and it was later found the batteries were being swapped by thieves on site.

Test the batteries before a unit goes in for service, and then after it comes back. Also, if a scooter goes in for service, and the batteries are reported as suspect, then ask that the batteries be left as they are for now (unless, of course, you have already proved them as shot!). On collecting the scooter check for the secret mark before the scooter is removed from the service centre.

If proven that a concern is falsely claiming battery failure, then spread the word. No-one can claim against the truth of your own experience! Such people deserve to have severe damage done to them, especially as they are definitely up to no good. Stories of charging a customer for new batteries when all that was done was to wipe them over with a rag and call them new are not uncommon.

This is not to be construed as a complete overview of battery maintenance - one needs a book for that - but at least a simple overview of what to look out for. Please feel free (and I urge you also) to get expert help if you feel something is not right. The aim here was to show that simple tests are well within the grasp of owners of battery powered machinery.

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© 18.10.02